Generally as example physical quantity measuring apparatuses a speed sensor, an acceleration sensor, an angular speed sensor, a magnetic sensor, a geomagnetic sensor, an azimuth sensor, an electronic compass, a temperature sensor, and a pressure sensor are well known. Respective sensors perform a predetermined signal processing on a signal based on a physical quantity output by a physical quantity signal output apparatus for obtaining information from the exterior, thereby measuring a target physical quantity. Microphones are also sensors that detect sound, i.e., vibrations of air, and are included in the physical quantity measuring apparatuses.
Signals output by the physical quantity signal output apparatus may include noise signals non-related to a target physical quantity. Hence, by performing a correction of reducing noise signals from a signal output by the physical quantity signal output apparatus, a target physical quantity can be further highly precisely measured. An example method of eliminating noise signals from the signal output by the physical quantity signal output apparatus is updating a coefficient of a first filter based on an output signal by a second filter having a faster speed than that of the first filter.
FIG. 1 is a block diagram for explaining a conventional physical quantity measuring apparatus which is disclosed in FIG. 12 of Patent Document 1. A physical quantity measuring apparatus disclosed in Patent Document 1 relates to a signal processing apparatus applied to a microphone array processing apparatus which suppresses disturbance noises using a microphone array for inputting a speech in a speech recognition apparatus or a television conference apparatus, etc., and which extracts a speech represented by a target signal. A first adaptive filter 1 includes a filter unit 11-1 that performs a filter computation on a reference signal x to obtain an output signal y1, a subtractor 12-1 that subtracts the output signal by the filter unit 11-1 from a desired response d to obtain an error signal e1, and an adaptive mode control unit 14-1 and a filter update computing unit 15-1 which update the filter coefficient of the filter unit 11-1 based on the reference signal x and the error signal e1. The output signal by the first adaptive filter 1 is taken as an output by the signal processing apparatus.
Moreover, a second adaptive filter 2 employs an adaptive filter configuration based on a typical NLMS algorithm, and includes a filter unit 11-2 that performs a filter computation on the reference signal x to obtain an output signal y2, a subtractor 12-2 that subtracts the output signal y2 by the filter unit 11-2 from the desired response d to obtain an error signal e2, and a filter update computing unit 15-2 that performs a computation of a filter update based on the reference signal x and the error signal e.
The second adaptive filter 2 has an adaptive speed set to be faster than that of the first adaptive filter 1, and the adaptive mode control unit 14-1 controls the adaptive speed of the first adaptive filter based on the output signal power by the second adaptive filter 2.
According to such a configuration, a signal processing apparatus can be realized which utilizes an adaptive filter that surely enables an adaptive operation without causing the target signal to be distorted and performing an adaptive operation on background noises.
Patent document 2 discloses an azimuth information apparatus, and includes a three-dimensional magnetic sensor and posture data corresponding to a posture of the magnetic sensor. This apparatus selects the smoothing intensity of a smoothing filter that performs smoothing on data of an azimuth angle derived from magnetic sensor data and the posture data based on the posture data at a time when the magnetic sensor data is obtained.
Patent Document 3 also discloses an azimuth information apparatus and an electronic compass which selects an algorithm for an azimuth calculation based on information on a geomagnetic intensity obtained right before and information on a current geomagnetic intensity, or azimuth information obtained right before and current azimuth information, thereby reducing the effect of magnetic noises.